Symptomatic loose bodies of the knee located in a popliteal cyst

Locating loose bodies in a knee arthroscopically can be challenging. Common locations for loose bodies to hide include the lateral and medial gutters as well as under the menisci. In 1986, Fergusson and Burge reported a single case of a loose body intermittently traveling between the intracapsular space and an extracapsular popliteal cyst. This article describes a similar event involving a 22-year-old man. Our patient experienced recurrent symptomatic loose bodies in the knee requiring previous knee arthroscopies. Most recently the patient had a radiographically documented and clinically symptomatic intra-articular knee loose body prior to surgery. Initial basic diagnostic knee arthroscopy did not reveal the loose body. On further arthroscopic evaluation of the posteromedial compartment of the knee, a capsular opening to a popliteal cyst was discovered. An accessory posteromedial portal was then used to directly visualize the contents of the cyst. Three loose bodies capable of traveling between the cyst and the joint were discovered. Transillumination allowed for safe localization of the cyst and subsequent percutaneous removal of the loose bodies under direct arthroscopic visualization.We recommend direct arthroscopic visualization of the posteromedial and posterolateral compartments of the knee when a known loose body cannot be located during basic diagnostic knee arthroscopy.